Headphone Sensitivity & Power Requirements

[Ken Tajalli]

I have had some heated discussions (disagreements!) with a fellow member regarding this issue. I believe it deserves a discussion of its own.
If there are similar threads, or it has already been discussed to death, I apologize, please point me to them.

There are sensitivity values given for headphones, it is given as dB for 1mW or dB for 1V RMS.
The general attitude, and a mathematical one! Is, to use this figure and calculate, how much power is needed to achieve a healthy loudness of say 115dB. Then we can safely say, this headphone needs an amp that can produce this much power.
Straight forward, makes sense! No?

I say No!
And that is the gist of my disagreement with my fellow member.
My arguments against:
- First see this

I have stated among my many arguments previously, that measurements for Electronic devices (DACs, Amps) can be absolute, but when it comes to Transducers, it is not.
Firstly we should recognize that, the sensitivity values given, are just an indication-tool, used for comparison.
Take two headphones for example, one has a dip in its FR curve at 400Hz, the other has a peak at the same frequency. Do you think if I pick 400Hz to measure the sensitivity, the value I get, is going to be reliable?
Secondly, in the scope of calculating how much power is needed, Loudness is a subjective value.
It depends on the type of music being played, the FR of the DUT, aaaand . . . , the hearing of the listener's ears.
Power and Gain are also inter-related. Higher power amps have more gain, and sometimes, we may need the gain, and not necessarily the max. power. With headphones, people equalize. If you equalize Bass frequencies, you need to use pre-cuts, right?
The amp being used, can quickly run out of power at bass, and overall loudness suffers. Now what if we didn't EQ the bass, but we EQ the mids up? Now we don't need to use a pre-cut, Our ears are sensitive to the mids, so the headphones will become louder with the same power capability.
Finally, someone with a failing hearing, will need more power to Hear better.
So I state that calculating (guessing) power requirement for headphones, is not as straight forward as some believe. It is complex, with variables depending on case to case surroundings.
What do you think?

 

[DVDdoug]

IMO, the bigger issue is that power also depends on impedance. Headphone impedance has a very wide range and a headphone amp that can put-out 1W at 32 Ohms may not be able to put-out 1W at 300 Ohms. With a power amplifier it's easier because you can specify power at 4 & 8 Ohms.

I'd prefer a voltage spec.

I believe sensitivity is usually specified at 1kHz.

 

[solderdude]

Take two headphones for example, one has a dip in its FR curve at 400Hz, the other has a peak at the same frequency. Do you think if I pick 400Hz to measure the sensitivity, the value I get, is going to be reliable?

No it will not be useful but also not useless as the difference will likely just be a few dB max.
Add to that the fixture must be calibrated as well. Add to that product tolerance/variance.

Also know that manufacturers sensitivity and or efficiency numbers often are incorrect. Yes, also from the big manufacturers.
Furthermore it is mostly unknown at which frequency (or frequency band) it is measured and on what gear and if this was a prototype or production type.
Often just dB is mentioned or dBmW is listed but somehow a dBV value is used (or v.v.).
It is a mess.

To calculate needed 'power' this number needs to be correct.

Secondly, in the scope of calculating how much power is needed, Loudness is a subjective value.
It depends on the type of music being played, the FR of the DUT, aaaand . . . , the hearing of the listener's ears.

Yes, depends on DR, and how loud it is recorded and the frequency response of the headphone as well as the applied EQ (if needed).
To calculate the power you will also need to know the impedance.
Better to use dBV if you want to compare headphones and calculations.

I built myself a handy meter that, when one knows the sensitivity (dBV) can instantly calculate peak SPL and see what peak voltages were present.
The meter is very fast and has 'peak hold'.

I gauge the sensitivity of a headphone by looking at the 'average' level of mids (and a bit of the bass) and for reference I use a HD650 of which I know the sensitivity and know which voltage is applied.

Due to the 'wobbly' nature of a headphone's frequency response it may not be the best idea to measure at 400Hz or 1kHz only as there may be dips or elevations at that point relative to the 'average' SPL.

 

[Ken Tajalli]

No it will not be useful. Add to that the fixture must be calibrated as well. Add to that product tolerance/variance.


Yes, depends on DR, and how loud it is recorded and the frequency response of the headphone as well as the applied EQ (if needed).
To calculate the power you will also need to know the impedance.
Better to use dBV if you want to compare headphones and calculations.

I built myself a handy meter that, when one knows the sensitivity (dBV) can instantly calculate peak SPL and see what peak voltages were present.
The meter is very fast and has 'peak hold'.
View attachment 390226

Excellent!
Also not forgetting that not every amp can drive low impedance loads. Some may clip or go into protection given a low impedance.
So even a dBV should be viewed in that regard.

 

[NTK]

Excellent!
Also not forgetting that not every amp can drive low impedance loads. Some may clip or go into protection given a low impedance.
So even a dBV should be viewed in that regard.

Amir's charts of distortion+noise vs output voltage for a range of loads give that information.

 

[solderdude]

Specs should best be given in dBV where it is meant the measured SPL when 1V is applied.

Fortunately, after calculating the found voltage of Amir's measurements (400Hz, 94dB SPL) to dBV I often find his measurements are largely in agreement with mine (within tolerance range).

 

[Joachim Herbert]

On a side note, 115 dB is all but a healthy level.

 

[Ken Tajalli]

On a side note, 115 dB is all but a healthy level.

Sort of!
115dB peak is about 95dB or so, average listening.

 

[solderdude]

115dB momentary peaks in music with a DR>15 and only for a song is something entirely different than an average noise level of 115dBA.

The thing is that IF one every now and then likes to turn up a song really loud for a short moment and don't want any clipping it is best to have an amplifier that can supply enough voltage to reach that level.
It is also a good idea to test headphones in the lowest frequencies at that level to see how well they respond to that.

For instance... the FiiO FT1 is 117dBV and a (non E.U.) phone can supply 1V. Most dongles even can supply 2V.
Putting it on my head and listening to 'all evening relaxing levels' in other words soft level I measure peaks of 30mV (87dB peaks, with DR12 song = 75dB average).
Listening to more 'active' listening levels (during the day trying to evaluate sound quality) I measure 200mV peaks (102dB peaks)
Listening to loud levels that are 'tolerable' for a minute or so I measure 700mV peaks (114dB peaks with DR17 recording = 97dB average, dBA will be a lower value).

My HD800 (with EQ) requires about 14dB (5x) higher output voltage for the same listening levels.

 

[oleg87]

Simply factor in a healthy margin to your listening volume so you don't have to worry about the vagaries of sensitivity measurements.

 

[Ken Tajalli]

Simply factor in a healthy margin to your listening volume so you don't have to worry about the vagaries of sensitivity measurements.

"Margin" to what?
That's the question!
My LCD-XC connected to my Hugo2 has a healthy margin, with a Susvara?, that would be a different story.
Headphone power, specially on portable devices, comes at a premium.

 

[solderdude]

I wrote an article about sensitivity, efficiency, power ratings and what power is needed (and how to find out what a headphone owner needs).
It might be of interest to folks who always wondered about this subject.

sensitivity & efficiency & more

homeback to learn published: Jul-02-2025 Not all headphones play equally loud on the same volume control setting when connected to the same device.There is a number that gives information about how…

diyaudioheaven.wordpress.com

 

[TRDK]

Based on:

Headphones power calculator

Find the best headphones, speakers and home audio. 365-day returns, free shipping over $100 and legendary customer service!

headphones.com

and

I did some calculations with:

 

[solderdude]

Acc to Amir's measurements the Noire X is 103dB/V and not 112dB/V
Amir measured the E3 = 100dB/V instead of 112dB/V so something is not right.
The calculator itself works correctly so the dBmW numbers are incorrect.
This is exactly what my article is about.

 

[amirm]

What do you think?

You did a very good job of covering it. The only thing I would add is that going from loud to very loud takes incredible amount of extra power. The last quarter range of most headphone amps brings very little loudness. The math is exponential and works against you.

Related, you can get decent amount of loudness out of just about anything. It is going beyond that which requires a beefy amp.

Finally, you may buy other headphones in the future. The amp, you want to buy and be done with it.

 

[TRDK]

Acc to Amir's measurements the Noire X is 103dB/V and not 112dB/V
Amir measured the E3 = 100dB/V instead of 112dB/V so something is not right.
The calculator itself works correctly so the dBmW numbers are incorrect.
This is exactly what my article is about.

Benchmark has this tool:

Headphone Sensitivity Converter

Convert headphone sensitivity from dB SPL at 1 mW to dB SPL at 1 Vrms. Convert headphone sensitivity from dB SPL at 1 Vrms to dB SPL at 1 mW.

benchmarkmedia.com

For Noire X it shows 112dB/V

 

[solderdude]

The tools on their website are fine and calculates correctly.
It is the input in the tool that is the culprit and that may well be my fault (partly) as in my list I state it is 94dB/V (75dB/mW) and it looks like the dB/V and dB/mW have been swapped somewhere and what part of my article is about,.
I also got the numbers from somewhere (if I or Amir did not measure it) so that's where the number comes from.
I know Amir's measurements are correct as my measurements usually are within 1dB of those of mine.

Will have to add new models and fix my table one of these days but that is a lot of work.

 

[TRDK]

I totally trust @Amir - he is doing a great job.

I just find it very strange that the different calculation tools for Noire X (impedance flat) shows 112.9 dB/V but you state 103 dB/V

in my list I state it is 94dB/V (75dB/mW) and it looks like the dB/V and dB/mW have been swapped

Based on these figures I did a calculation based on 110dB loudness, than one would need 3.0624 W for Noire X.

I am using JDS Labs Element IV that has 2.3 W (6.11 VRMS) @16 Ω (settings: low gain -10 dB, headroom -4dB, -18 dB LUFS) with Noire X and have absolutely no problem.

And, if something has been swapped, wouldn't it than be a good a idea if you told them that? Many people are using the tool

Headphones power calculator

Find the best headphones, speakers and home audio. 365-day returns, free shipping over $100 and legendary customer service!

headphones.com

 

[solderdude]

You did a very good job of covering it. The only thing I would add is that going from loud to very loud takes incredible amount of extra power. The last quarter range of most headphone amps brings very little loudness. The math is exponential and works against you.

Related, you can get decent amount of loudness out of just about anything. It is going beyond that which requires a beefy amp.

Finally, you may buy other headphones in the future. The amp, you want to buy and be done with it.

added this to the article and may elaborate a bit more later on:

When someone owns more than one headphone or expects to buy other ones in the future it may pay to buy an amplifier that can supply enough voltage and current (so power in various impedances) so that all headphones can be properly driven to loud levels without ever hitting clipping levels.
This could, however, lead to owning an amplifier that is capable of delivering way too much power in certain high-efficiency head-/ear-phones (the 20mW / 30mW rated ones) and accidentally blow the drivers in an unforeseen situation.

Also... one should realize that most headphones have a sensitivity number between 95dB/V and 115dB/V which basically means that 1V will be enough to make them play loud enough for listening to music at 'comfortable loud' listening levels.

The crazy power levels (> 0.5W) are really only needed when one wants to play really, really LOUD without an amp clipping and even then this is really only needed for a few insensitive (inefficient) headphones.
It is good to realize that when one wants to play music about twice as loud one needs 10dB more power.
This also means 10x more power. When one wants go twice as loud again you need 10dB more power yet again thus requiring 100x more power (20dB more) in total.
Below a table that shows what power increase is needed for a certain level increase.
1dB is just noticeable, 3dB is a doubling of power and 6dB a doubling of voltage. Both of these are easily audible. 10dB is close to a perceived doubling of loudness (sound intensity)

When realizing that most headphones are in the 90dB/mW and 100dB/mW efficiency range is easy to see that to reach 110dB (peaks), which is already loud, only 10dB to 20dB is needed so 10mW to 100mW is usually more than enough to play really loud.
One only needs a LOT of power for the rare inefficient headphones (80dB/mW range) or when one has a fairly inefficient headphone and wants to play uncomfortable loud (120dB peaks).


amplifier output resistance


All amplifier circuits also have an output resistance (impedance actually).
A resistance implies that the current and voltage are directly related in amplitude and phase for all frequencies.
An impedance is more complex 'resistance' and the voltage and current may not be in phase and may differ per frequency as well.

The same is true for the loads (i.e. headphones/speakers).
There are not many headphones (nor speakers) that behave like a 'pure resistance' in the audible frequency range. Most headphones/speakers have a varying impedance.
It is this varying impedance (especially low impedance) in combination with a higher than several Ω output resistance amplifiers that causes tonal changes in headphones.
More info about this aspect can be found HERE.

Most portable devices have a very low output resistance/impedance as do most of the current headphone amps and DAC/amp combinations.
However, there are a few amplifiers that have a higher output resistance. The problem is that most spec. sheets do not mention the output resistance and often only 'report' for which headphone impedance range that device is suited.
External USB sound cards with headphone out also can have a higher output resistance up to 50Ω or so.
The highest output resistance is found in some (OTL) tube amplifiers and above all on integrated amps, receivers and even some AV-Receivers. The 'headphone out' of such devices, more often than not, consists of the speaker out signal simply attenuated with some resistors to pad the voltage down.
Output resistance of such outputs can be anything between 50Ω to 600Ω and are bound to change tonality of quite a few headphones.

 

[solderdude]

And, if something has been swapped, wouldn't it than be a good a idea if you told them that?

If I would need to correct every single mistake found on the web I would not have any time left.
It is the responsibility of the one posting the info to ensure it is accurate.
Of course ... I need to update my 'list' (have put that on my to-do list) which is my responsibility but in many cases I can only go of numbers found on the web and by manufacturers. The latter often post incorrect numbers or fail to mention dB/mW or dB/V.


113dB/V means it would play VERY loud even directly from an E.U. phone... and these headphones don't do that.
The problem is that Dan does not give sensitivity/efficiency specs.

With 103dB/V you can reach 118dB peaks on your amp which is uncomfortable loud so yes... you would have no issues driving the noir to very loud levels.